Beyond 3G and Toward 4G Networks

Beyond 3G and Toward 4G Networks
In the last few decades, the telecommunications industry has become especially responsive
to market demands for new services and capabilities. This has been particularly
true of the wireless segment of the industry, which has seen vigorous growth from
cordless phones and first-generation analog cellular networks through 2G digital networks,
low-speed mobile data networks, paging systems, and now 3G technologies
that provide improved voice quality and integration of data and voice services. It has
always been difficult to predict the future of the wireless communications industry, but
there are certain trends that one can discern and try to project.
WAN and WLAN Integration. With respect to the critical issue of spectrum allocation
and administration, we see 3G systems operating in licensed bands, where service
providers must make large investments to secure access to those licenses. On the other
hand, WLANs and WPANs operate in unlicensed bands, where one does not need
to purchase spectrum and where the user is unencumbered by regulatory rules and
regulations. However, there is also no regulatory control of signal interference in the
unlicensed bands, and thus connectivity and link performance can often be problematic.
It would not be wise to predict that all wireless communications will migrate
to unlicensed bands, but it is accurate to say that the last several years have witnessed
a renewed interest and vigorous growth in the use of unlicensed-band systems.
One possible migration path is the eventual integration of WANs with WLANs in
unlicensed bands.
Ad Hoc Networking. Another important evolving technology is ad hoc networking,
which uses a distributed network topology (see Chapter 11) and has the capability for
network reconfiguration without the need for a geographically fixed infrastructure. This
technology was developed for military networking requirements but has found some
application in commercial voice and data services. The ad hoc networking topology is
suitable, as an example, for rapid deployment of any wireless network in a mobile or
fixed environment. UWB and S-T Coding. It is clear that CDMA is emerging as the preferred transmission
technology for 3G systems, providing enhanced voice quality and increased
network capacity relative to 2G systems, while OFDM has been adopted in WLANs
operating at 5 GHz. It is safe to project that OFDM will continue to play an important
role in the future of broadband wireless access. Other important emerging technologies
include ultrawideband (UWB) communication and space-time (S-T) coding. TheUWB
concept (see Chapter 12) uses transmission of narrow noiselike pulses with spectrum
extending over several gigahertz and offers promise of supporting very large numbers
of simultaneous users [Sch00]. The S-T coding concept was devised to improve performance
and increase spectrum utilization efficiency on bandlimited wireless channels
by combining channel coding, modulation, transmitter diversity, and optional receiver
antenna diversity.
Location Awareness. Another evolving technology is position location, and there is
particular interest now in indoor applications (see Chapter 13). Examples of how this
technology can be beneficial include location of patients, medical professionals, and
instrumentation in a hospital; location tracking of merchandise in a large warehouse;
and tracking of systems and components in a large factory. Other potential applications
include personnel location in military, firefighting, and disaster-recovery situations. It is
expected that this technology will become an integral part of future wireless networks.
In the United States, the FCC has already mandated the integration of position location
systems with cellular networks (e.g., for E-911 services), although the extent and
method of integration is not yet clear.
Infrastructure-Based and Ad Hoc Access. It is useful to distinguish between two
aspects of evolving broadband access technology: infrastructure-based access technology
and ad hoc access technology, distinctions based on network topology. In
infrastructure-based broadband access, the network includes a fixed (wired) infrastructure
that supports communication between mobile terminals and between mobile
and fixed terminals. A typical example is a WLAN employing one or multiple access
points (APs), with APs connected by a wired (typically cabled) backbone. Two mobile
stations in the same AP coverage area will communicate through that AP, and widerarea
connectivity is supported by AP-to-AP communication over the wired backbone.
A common example of infrastructure-based broadband access is a WLAN based on
the popular IEEE 802.11b standard, operating in the 2.4- to 2.497-GHz ISM band,
providing broadband access to the Internet at data rates of 1, 2, 5.5, and 11 Mb/s.
Since adoption of the 802.11b specification in July 1999, 802.11a and 802.11g have
been developed to provide steadily increasing data-rate options. Currently, 802.11n is
under development to provide the next step in available data rates. Some manufacturers
are proposing the use of 40 MHz of bandwidth, up from 22 MHz in the 802.11b/g
specifications, for the new specification.
In Europe, the high-performance radio LAN (HIPERLAN) standards evolved out
of the earlier wireless ATM initiative of the ATM Forum [Ray92]. The HIPERLAN1
specification, completed in 1997, uses the same modulation technique, OFDM, as
IEEE 802.11a, both standards operating at 5 GHz. The HIPERLAN1 standard was not
widely adopted by manufacturers and is generally considered an unsuccessful standard.
Subsequent ETSI efforts led to the HIPERLAN2 standard, which bears many similarities
to IEEE 802.11a and provides a series of data rates up to 155 Mb/s, rates approaching the capabilities of wired LANs. Unlike 802.11a, HIPERLAN2 includes
features better suited to supporting not only data traffic but also time-critical services
such as packetized voice and multimedia service. These aspects of the HIPERLAN2
specification lend themselves to integration of data, voice, and multimedia services. A
key objective in the HIPERLAN2 standardization effort was to provide seamless interoperability
of different wireless networks, including 3G networks. However, it appears
that the HIPERLAN standards have been overtaken by the IEEE 802.11 standards.
In ad hoc networking, the network is reconfigurable and can operate without the
need for a fixed infrastructure. This is sometimes referred to as distributed-network
topology. Such networks are used primarily in military communications, but have also
found application in some commercial networks for voice and data transmission. Ad
hoc networks may employ either single-hop (peer-to-peer) or multihop connectivity.
By way of example, the 802.11 WLAN standards support single-hop peer-to-peer ad
hoc networking. When an 802.11 terminal is powered up, it first searches for a beacon
signal transmitted by an access point or another terminal announcing the existence
of an ad hoc network. If no beacon is detected, the terminal takes the responsibility
of announcing the existence of an ad hoc network. Also, several other wireless
technologies, such as the Personal Handyphone System (PHS) and the NEXTEL satellite
network, utilize peer-to-peer push-to-talk communication to establish connection
between pairs of voice terminals.
Important emerging areas for application of ad hoc networking technology include
wireless personal-area networks (WPANs). At present, the wireless industry differentiates
WPANs from WLANs by their smaller signal coverage area, ad-hoc-only topology,
low power consumption, plug-and-play architecture, and support of both voice and data
devices. The earliest WPANs were BodyLANs, developed by the U.S. Department of
Defense to connect sensors and communications devices carried by a soldier or attached
to a soldier’s clothing. Commercial applications of the same technology can provide
connectivity among laptops, notepads, and cellular phones carried by the business traveler.
Motivated by the BodyLAN project, the IEEE in 1997 formed the WPAN study
group as part of the 802.11 standardization activity. In 1998 the WPAN group was
expanded by the inclusion of two related initiatives, HomeRF and Bluetooth. Also
in 1998, a special Bluetooth group was formed within the WPAN group [Sie00]. In
March 1999 the 802.15 group was formed as a separate group within the IEEE 802
structure to handle WPAN standardization. Subsequently, Bluetooth was selected as
the base specification for IEEE 802.15. In Section 2.4 we provide further details on
the role of WPAN, HomeRF, and Bluetooth in the evolution of the WLAN industry.